1. Field of the Invention
This invention relates to a digital display clock and in particular to the digital type clock in which the time is displayed on a plurality of tilting leaf plates or on the cylindrical surface of drums which is driven with uniform rotation transmitted from a means for generating time signals.
2. Prior Art
It has been well-known that there have been various digital display clocks in which an oscillator is used as the means for generating time signals, or in which a plurality of tilting leaf plates with printed time figures thereon or the cylindrical surface of the drums with printed time figures thereon is driven by AC synchronous motor as the means for generating time signals. In a conventional digital clock uniform rotation of the driving section is changed into an intermittent and segmental rotation corresponding to each time indication by means of a so-called Geneva-gear mechanism so that the number of displaying leaves for each indicating division can be reduced. In a normal digital display clock, the Geneva-gear mechanim is palced between indicating sections, for example, between a minute wheel and a hour wheel. Consequently, in the prior art system the display area in the front is reduced and the space between one-minute, ten-minute and hour indicating leaves is widened in comparison with the total body size of digital clock because of use of the Geneva-gear mechanism. Such limitations cause an affect upon the display and provides some restrictions in the design. There is another drawback in the composition of indicating sections since the reduction ratio of Geneva-gear mechanism cannot be designed very small in the prior art system; that is the normal Geneva-gear can only provide a ratio of 12 to 1 at the least. In the prior art system, the minute indicating leaves cannot be divided into one-minute indications and ten-minute indications, which must have a small reduction gear ratio, and such a means is adopted that 60 leaves must be mounted on single minute indicating wheel at the least and that one leaf must be moved every one minute. If the cylindrical drum system is adopted, the minute indication is driven by a uniform rotation instead of an intermittent segmental motion and the hour indication is only driven by an intermittent rotation. Such a prior art system suffers from several defects. Processing and assembling of such system is complicated and expensive due to the comparative increase in the number of leaves in the leaf type of digital clock. The display is hard to be read due to the fact that the figures are fairly small printed on the cylindrical surface of drum in the drum type digital clock. Furthermore, the prior art system in which the reduction ratio of Geneva-gear mechanism which restricts the design of a 24 hour display clock is fatally disadvantageous in alarm system, timer, kitchen timer, etc.
The above-described drawbacks are caused by employment of individual time indicating wheels themselves as a part of the Geneva-gear mechanism which is used as the intermittent reducing transmission mechanism among individual time indicating wheels, which affects and retricts display area and reduction gear ratio.